High side drivers are widely used to control grounded electrical loads in, for example aerospace, automotive and industrial applications. High side drivers have been applied to driving the high side of power On/Off relays, RF switches, solid state relays and switches, and other grounded loads from a positive direct current (DC) voltage source. The loads may be characterized as resistive, inductive, capacitive, or a mix thereof. A high side driver may, for example, include one or more source drivers that provide switching (and, if desired, other control functions) between the high (positive) side of a power source, and a first terminal of an electrical load being switched, where a second terminal of the electrical load is connected to a common power circuit ground.
A fault in the electrical load (“load fault”), such as a short circuit condition or a partial short, may create a high current condition that damages the load and/or nearby components and equipment. The high current condition also has the potential to damage a source driver, and/or the high side driver. Known techniques such as fuses and circuit breakers provide reliable protection, but are unattractive for many applications where self-resetting of the high side driver and/or load is desirable.
Current limiting techniques have been employed in laboratory power supplies as well as commercially available integrated circuits such as INFINEON Smart Highside High Current Power Switch Reference BTS50055-1TMC, and ALLEGRO Protected Quad Driver with Fault Detection and Sleep Mode Reference A2557. The above-mentioned devices provide for progressive current limitation, wherein an output voltage of a high side driver is progressively limited in the event of a partial or total short, so as to assure that load currents do not exceed a specified level. An example of progressive current limitation, as the term is used herein, is illustrated in FIG. 1. For such a progressive current limitation scheme, a source driver output voltage is normally regulated, within a prescribed tolerance, in the absence of a fault condition, over a range of normal load impedances, as illustrated in FIG. 1, “pre-fault period” and “post-fault period”. During the existence of a fault condition (i.e., the load impedance drops below a specified limit), the source driver output voltage is progressively decreased, so as to prevent load current from exceeding a specified level, as illustrated in FIG. 1, “fault condition”.